[Role of microtubules in adrenal gland steroidogenesis]

In order to determine the role of the microtubular network in adrenal steroidogenesis, we have studied the effect of vinblastine, a potent antimicrotubular agent on corticosteroid secretion by frog adrenocortical fragments in perifusion. Administration of vinblastine (10(-5) M) did not alter the spontaneous secretion of corticosteroids and had no effect on the steroidogenic response to angiotensin II and prostaglandin E1. In contrast, vinblastine induced a marked decrease in ACTH-induced stimulation of corticosteroidogenesis. To investigate further the site of action of the microtubular system in ACTH-induced steroidogenesis we have studied the effect of vinblastine on the different steps of the stimulation of the adenylate cyclase system. Our results show that vinblastine does not alter the stimulatory action of cAMP, the second messenger of ACTH. In addition, the corticosteroidogenic effect of forskolin and NaF (which respectively stimulate the adenylate-cyclase subunit and the guanyl nucleotide regularly protein) was not affected by vinblastine. These results indicate that the microtubular network interferes in the coupling of the secretory response of the adrenal glands to ACTH, either at the level of the binding of ACTH to its receptor or in the coupling of the receptor to the guanyl nucleotide regulatory protein.